Implementing cable failover in multiple cable PCI express IO interconnections

ABSTRACT

A method, system and computer program product are provided for implementing cable failover in multiple cable Peripheral Component Interconnect Express (PCIE) IO interconnections to an external IO enclosure. System firmware is provided for implementing health check functions for the PCIE IO interconnections to identify a faulted low byte cable. A cable failover mechanism recovers a PCI link to the external IO enclosure. A multiplexer logic is provided between the PCIE host bridge (PHB) and the cable connected to the IO enclosure to perform a full lane reversal of the PCIE lanes.

This application is a continuation application of Ser. No. 14/924,617filed Oct. 27, 2015.

FIELD OF THE INVENTION

The present invention relates generally to the data processing field,and more particularly, relates to a method, system and computer programproduct for implementing cable failover in multiple cable PeripheralComponent Interconnect Express (PCIE) IO interconnections.

DESCRIPTION OF THE RELATED ART

Peripheral Component Interconnect Express (PCIE) has become the industrystandard IO bus for server computer systems, as well as personalcomputers (PCs). Traditionally, servers install PCIE IO adapters (IOAs)in slots within a system unit that connect through a PCI host bridge tothe system memory and processor buses. IBM POWER and Z series systemshave offered external IO enclosures to provide additional PCIE slotsbeyond those that are available within the system unit. These have inthe past been connected to the system unit through IBM proprietaryinterconnect architectures such as HSL and Infiniband 12X IO loops onIBM POWER systems.

A typical PCIE bus is a simple board path from the PCIE host bridge(PHB) and the IO adapter (IOA). When using optical cables for attachingan external IO drawer the complexity of the path is greatly increasedwith the various components in the path which include PCIE retimers,optical transceivers (CXPs) that convey PCIE signals over opticalchannels and cables. The components in this optical path do not alwayshave clear failure mechanisms that can be used to help determine wherethe fault in the PCIE path is to indicate to firmware what opticalchannels are at fault.

A need exists for an effective and efficient mechanism for implementingcable failover in multiple cable Peripheral Component InterconnectExpress (PCIE) IO interconnections in a computer system.

SUMMARY OF THE INVENTION

Principal aspects of the present invention are to provide a method,system and computer program product implementing cable failover inmultiple cable Peripheral Component Interconnect Express (PCIE) IOinterconnections in a computer system. Other important aspects of thepresent invention are to provide such method, system and computerprogram product substantially without negative effects and that overcomemany of the disadvantages of prior art arrangements.

In brief, a method, system and computer program product are provided forimplementing cable failover in multiple cable Peripheral ComponentInterconnect Express (PCIE) IO interconnections to an external IOenclosure. System firmware is provided for implementing health checkfunctions for the PCIE IO interconnections to identify a faulted lowbyte cable. A cable failover mechanism recovers a PCI link to theexternal IO enclosure. A multiplexer logic is provided between the PCIEprimary host bridge (PHB) and the cable connected to the IO enclosure toperform a full lane reversal of the PCIE lanes.

In accordance with features of the invention, when the entire low bytecable (PCIE lanes 0-7) has failed or is unplugged, the full lanereversal of the PCIE lanes of the high byte and the low byte cableenable recovery. PCI express requires the lanes to be functional insequential order, so if PCI lane 0 is not functional then a functioningPCI connection to the downstream device is not enabled.

In accordance with features of the invention, the lanes are changed froma 0-15 configuration to 15-0. The result of this configuration change isthat PCIE lanes 0-7 are now carried in the functional high cable and canform a functional PCIE link.

In accordance with features of the invention, the PCIE link runs withhalf the normal configuration in a degraded state, but allows theconnection to function until the customer is able to service the faultycable and restore full width.

In accordance with features of the invention, firmware detects throughhealth check failures in the low cable to determine when lane reversalshould be provided.

In accordance with features of the invention, the PCIE lane multiplexersare configured to reversed mode and the PCIE links are retrained to thedownstream device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiments of the invention illustrated inthe drawings, wherein:

FIG. 1 illustrates an example computer system for detecting status andsparing of optical Peripheral Component Interconnect Express(PCI-Express or PCIE) cable channel attached to an IO drawer andimplementing a sideband control structure for Peripheral PCIEinput/output (IO) expansion enclosures or IO drawers in accordance witha preferred embodiment;

FIGS. 2A, and 2B illustrates cable card and sideband controls of theexample system of FIG. 1 in accordance with a preferred embodiment;

FIGS. 3A, and 3B illustrates further details of Local and Remote FPGAControllers of the example system of FIG. 1 in accordance with apreferred embodiment;

FIG. 4 illustrates example operational features of a physical layer viewof I2C multiplexer (MUX) and data engine at host side and IO drawer endof the example system of FIG. 1 in accordance with a preferredembodiment;

FIG. 5 is a flow chart illustrating example firmware operationalfeatures using sideband status information of the example system of FIG.1 in accordance with a preferred embodiment;

FIGS. 6A and 6B together illustrate example PCI bus topology of theexample system of FIG. 1 in accordance with a preferred embodiment;

FIG. 7 illustrate example lane sparing hardware of the example system ofFIG. 1 in accordance with a preferred embodiment;

FIG. 8 is a flow chart illustrating example operations for implementingcable failover in multiple cable Peripheral Component InterconnectExpress (PCIE) IO interconnections to an external IO enclosure inaccordance with a preferred embodiment; and

FIG. 9 is a block diagram illustrating a computer program product inaccordance with the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings, which illustrate exampleembodiments by which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In accordance with features of the invention, a method, system andcomputer program product are provided for implementing cable failover inmultiple cable Peripheral Component Interconnect Express (PCIE) IOinterconnections to an external IO enclosure in accordance with apreferred embodiment. System firmware is provided for implementinghealth check functions for the PCIE IO interconnections to identify afaulted low byte cable. A cable failover mechanism recovers a PCI linkto the external IO enclosure. A multiplexer logic is provided betweenthe PCIE primary host bridge (PHB) and the cable connected to the IOenclosure to perform a full lane reversal of the PCIE lanes.

In accordance with features of the invention, when the entire low bytecable (PCIE lanes 0-7) has failed or is unplugged, the full lanereversal of the PCIE lanes of the high byte and the low byte cableenable recovery. PCI express requires the lanes to be functional insequential order, so if PCI lane 0 is not functional then a functioningPCI connection to the downstream device is not enabled. In accordancewith features of the invention, the lanes are changed from a 0-15configuration to 15-0. The result of this configuration change is thatPCIE lanes 0-7 are now carried in the functional high cable and can forma functional PCIE link.

Having reference now to the drawings, in FIG. 1, there is shown anexample computer system generally designated by the reference character100 for implementing cable failover in multiple cable PeripheralComponent Interconnect Express (PCIE) IO interconnections to an externalIO enclosure in accordance with a preferred embodiment. Computer system100 includes a computer Central Electronics Complex (CEC) 102 thatincludes a system motherboard 104 common in the art that provides forthe physical packaging interconnection of the various componentsillustrated within the CEC 102. Computer system 100 includes aninput/output (IO) expansion enclosure or IO drawer generally designatedby the reference character 106 in accordance with a preferredembodiment.

In accordance with features of the invention, the IO drawer 106 is anelectrical enclosure that provides PCIE add-in card slots (PCIE slots)or integrated devices utilized by firmware and software operating withinthe CEC 102 to extend the number of PCIE devices physically configurablewithin the scope of the CEC.

CEC system motherboard 104 includes one or more processors or centralprocessor units (CPUs), such as processor 110. Processor 110 is suitablyarranged for executing firmware and software, such as operating systemand applications hosted by respective operating systems in control ofthe overall computer system 100 in accordance with a preferredembodiment.

CEC system motherboard 104 includes one or a plurality of PCIE rootcomplexes 120. Each PCIE root complex 120 includes one or a plurality ofPCIE host bridges (PHBs) 130, each PHB 130 providing a respective PCIElink 132 to a respective PCIE slot 134 mounted commonly on the systemmotherboard 104. For example, the PCIE link 132 is comprised of aplurality of 16 lanes of PCIE signaling wires and auxiliary signals,such as specified in the PCIE standard. The auxiliary signals includePCIE PERST, also called Fundamental Reset, and PCIE clocks from the PHB130 to a PCIE device, PCIE card present from a device to a PHB 130, andother such discrete signals that operate independently of the PCIEsignaling lanes.

One or more of the PCIE slots 134 includes a respective PCIE cable card140 including a PCIE lane multiplexer (mux) logic 141 connected with arespective PCIE cable connector 142 connected by a pair of PCIE cables144 to a corresponding respective PCIE cable connector 142 provided withthe IO drawer 106, as shown. While the PCIE lane multiplexer (mux) logic141 is shown with the cable card 140, it should be understood thepresent invention is not limited to this arrangement. For example, thePCIE lane multiplexer (mux) logic 141 advantageously could be providedinside the PHB 130. Also the PCIE lane multiplexer (mux) logic 141advantageously could be provided outside the PCIE switch 156 of afan-out module or fan-out bay 154.

In accordance with features of the invention, the PCIE lane mux logic141 contains PCIE lane muxes to reverse the PCIE lane assignments fromthe PHB 130 to the external PCIE cables 144 and logic to control themuxes through system firmware.

IO drawer 106 includes one or a plurality of module bays, such as adirect slot bay 150 including a plurality of PCIE slots 152, and afan-out bay 154, including a PCIE switch 156 connected to anotherplurality of PCIE slots 152, as shown. Each of the direct slot bay 150,PCIE slots 152, and the fan-out bay 154 is connected to the CEC 102 bythe individual and independent cables 144 via PCIE cable connectors 142,as shown. The PCIE switch 156 includes an upstream port 158 connectedupstream to the PCIE Cable Connector 142 and downstream to a pluralityof downstream ports 160, each connected to a respective PCIE slot 152,as shown.

In accordance with features of the invention, the downstream PCIEdevices, such as the PCIE switch or adapters 156 support the samemaximum lane width, such as 16 lanes, as the PHB 130. The downstreamPCIE devices or PCIE switch or adapters 156 support running in normal(0-15) and lane reversed (15-0) modes. downstream PCIE devices or PCIEswitch or adapters 156 support the PCIE lane reversal mode. Also thePCIE lane multiplexer (mux) logic 141 could be added to the direct slotbay 150.

In accordance with features of the invention, firmware detects, forexample, through health check failures in the low cable to determinewhen lane reversal should be provided. Firmware can configure the PCIElane mux logic 141 to a reversed mode and retrain the PCIE links to thedownstream device, such as PCIE switch 156.

Computer system 100 is shown in simplified form sufficient forunderstanding the present invention. The illustrated computer system 100is not intended to imply architectural or functional limitations. Thepresent invention can be used with various hardware implementations andsystems and various other internal hardware devices.

In accordance with features of the invention, one or a plurality ofcables 144 is provided with each cable card 140 and respective PCIE slot152 or PCIE switch 156. As shown, a pair of PCIE cables 144 convey PCIEsignal lanes and auxiliary signals forming a single PCIE link, and thePCIE cables 144 also convey sideband control and status signals betweenthe CEC 102 and the IO drawer 106. The use of two cables 144 for eachsingle PCIE link between the CEC 102 and IO drawer 106 advantageouslyenables redundancy in the event of a cable failure. Only a single cable144 is utilized in communicating sideband controls and status betweenthe CEC and IO drawer, and each of the two cables 144 provides analternative signaling path to communicate such sideband controls. Inaccordance with a preferred embodiment, the invention utilizes a pair ofcables to carry PCIE signals and redundant status and control signals.Other embodiments may utilize more than two cables to carry either orboth PCIE signal lanes and redundant sideband status and controlsbetween a cable card 140 in a CEC 102 and a slot 152 or switch 156 in anIO drawer 106. A plurality of cables forming a single link isadvantageous to provide sideband signal redundancy; however, otherembodiments may utilize a single cable, having spare optical channelswithin that single cable, to obtain the optical channel failure,sideband signal redundancy, and sparing objectives of the invention.

In accordance with features of the invention, the cables 144 may beconventional copper cables or fiber optic cables employingopto-electronic transceivers at each cable end. For example, withrelatively short distances, such as inches to a few feet, copper cables144 are generally suitable for conveying PCIE lanes operating atrequired PCIE signaling rates between the CEC 102 and IO drawer 106.Optical cables 144 advantageously provide electrical isolation to enablehigh signaling rates over longer distances, such as one to many meters.

In accordance with features of the invention, use of optical PCIE cables144 includes serializing required DC signals over the optical cables 144and then converting the serialized signals back to DC signals at theother end of the optical PCIE cables 144 at CEC 102 or the IO drawer106.

In accordance with features of the invention, firmware operating in theCEC 102 is enabled to determine a type of cable card 140 plugged into aPCIE slot 134, with a plurality of different such cable card typeshaving differing properties, such as whether the cables 144 are copperor optical, how many cables 144 emanate from the cable card 140, and thelike. It is similarly advantageous for firmware operating in the CEC 102to be able to determine whether the cables 144 are actually connected toan IO drawer 106, and what type of IO drawer 106, and the IO module bay150, or module bay 156, is connected to cables 144.

In accordance with features of the invention, in a logically partitionedcomputer system 100 firmware operating in the CEC 102 is enabled toassign respective CEC PCIE slots 134 to a particular logical partitionwhen that slot 134 contains a PCIE IO adapter. Computer system 100firmware operating in the CEC 102 is further enabled to detect a cablecard 140 in a PCIE slot 134 and to assign respective CEC PCIE slots 152of an IO drawer 106 to different logical partitions with the cable card140 connected to an IO drawer 106.

Referring also to FIGS. 2A, and 2B, additional example details of novelcable card 140 and sideband controls generally designated by thereference character 201 are shown of computer system 100 of FIG. 1 inaccordance with a preferred embodiment. As shown in FIG. 2A, includedwithin or accessible to the processor 110 is an Inter-Integrated Circuit(I2C) master device 202, which is the master of an I2C bus 204 utilizedas an IO bus of the sideband signaling apparatus of a preferredembodiment. It should be understood that other such IO buses or sidebandcontrol structures known in the art may be suitable to substitute forthe I2C bus 204 utilized by the invention. Within CEC 102, the I2C bus204 is connected between the I2C master device 202 and a card presentport expander 206, PCIE slots 134, a vital product data (VPD) chip 208,and a local control field programmable gate array (FPGA) 210 providedwithin the cable card 140.

The PCIE cable card 140 utilizes pins within the PCIE connector 142 ofthe PCIE slot 134 defined in PCIE as reserved pins to generate a signalidentifying the PCIE cable card 140 as a cable card. The card presentport expander 206 connected on the I2C bus 204 receives a card presentsignal from the cable card 140 uniquely indicating the presence of acable card, as opposed to a PCIE IO adapter. Firmware operating in theCEC 102 utilizes the I2C master 202 to read registers within the cardpresent port expander 206 in order to determine that the cable card 140is plugged in the respective PCIE card slot 134. It should be understoodthat devices other than the card present port expander 206 could be usedto receive cable card present information in a manner accessible tofirmware operating within the CEC 102.

The local control FPGA 210 includes registers that receive status fromand optionally signal controls to other hardware components located onthe cable card 140. The registers within the local control FPGA 210 areconnected to the I2C bus 204 proceeding from the PCIE slot 140 onto thecable card 140.

Referring also to FIG. 2B, the IO drawer 106 similarly includes a remotecontrol FPGA 250. The remote control FPGA 250 includes registers thatreceive signals from other hardware components internal to the IO drawer106. The IO drawer 106 includes a drawer controller 252 coupled to theremote control FPGA 250 via an I2C bus 254.

In accordance with features of the invention, as shown in FIGS. 2A, and2B, sideband controls 201 are coupled between the local control FPGA 210in the CEC 102 and the remote control FPGA 250 in IO drawer 106 by a lowbyte cable 260 and a high byte cable 262. For example, the low bytecable 260 conveys PCIE lanes 0 through 7 of the PCIE link from the PCIEslot 134, shown as Low Byte PCIE 264, and conveys sideband signalsbetween the cable card 140 and the IO drawer 106, shown as Low ByteControl 266. For example, the high byte cable 262 conveys PCIE lanes 8through 15 of the PCIE link from the PCIE slot 134, shown as High BytePCIE 268, and conveys sideband signals between the cable card 140 andthe IO drawer 106, shown as High Byte Control 270. For example, the highbyte cable 262 serves as an alternate or redundant connection to the lowbyte cable 260 for the purpose of conveying sideband signals.

Using either the low byte control 266 or high byte control 270, theremote control FPGA 250 signals changes in the states of varioushardware components or DC voltage signals within the IO drawer 106 tothe local control FPGA 210, which receives these changes in registersaccessible to firmware operating in the CEC 102. Similarly, firmwareoperating in the CEC 102 may set register values in the local controlFPGA 210 directed at the remote control FPGA 250 to change the state ofhardware components or DC voltage signals within the IO drawer 106.

Using the either the low byte control 266 or high byte control 270, thelocal FPGA 210 communicates local FPGA 210 register changes to theremote control FPGA 250. The registers within the remote control FPGA250 connect to the I2C bus 254 within the IO drawer 106. The remote FPGAregisters are also accessible as I2C devices from the local control FPGA210. Firmware operating in the CEC 102 utilizes registers in the localcontrol FPGA 210 to create I2C bus operations transmitted between thelocal control FPGA 210 and remote control FPGA 250 utilizing the lowbyte control 266 or high byte control 270. The local control FPGA 210enables firmware operating within the CEC 102 to determine variousconfiguration and operational states of hardware components or DCvoltage signals located on the cable card 210 as well as hardwarecomponents or DC voltage signals within the IO drawer 106.

The drawer controller 252 connected to the remote control FPGA 250within the IO drawer 106 monitors or manages states of the hardwareinternal to the IO drawer, such as turning on or off power supplieswithin the drawer, monitoring thermal or electrical states of componentswithin the drawer, taking actions in response to particular thermal orelectrical states or thresholds, and the like. The drawer controller 252connects to the remote control FPGA 250 utilizing the I2C bus 370,enabling the drawer controller 252 to read or write registers within theremote control FPGA 250 and to communicate status to or receive controlinformation communicated from the local control FPGA 210 using the lowbyte control 266 or high byte control 270.

Referring also to FIGS. 3A, and 3B, additional example details of localcontrol and remote control FPGAs 210, 250 are shown of the examplesystem 100 of FIG. 1 in accordance with a preferred embodiment.

The cable card 140 is shown connected to the IOA drawer 106 utilizing alow byte cable 302 and a high byte cable 304. The low byte cable 302conveys the low byte PCIE signals 306 representing PCIE lanes 0 to 7 andcontrol signals between the local FPGA 210 and remote FPGA 250 indicatedas low byte control 308. The high byte cable 304 conveys the high bytePCIE signals 310 representing PCIE lanes 8 to 15 and control signalsbetween the local FPGA 210 and remote FPGA 310 indicated as high bytecontrol 312. The signals conveyed by means of the low byte control 308and high byte control 312 signals may be communicated over either orboth of the low byte cable 302 and the high byte cable 304 at any onetime, such that each cable can convey the control signals as a backupfor the other in the event of failure or disconnection of one cable 302or 304, and such that signals may be communicated simultaneously overboth cables in order to detect the location to which each cable isconnected at the IO drawer 106.

The low byte control 308 and low byte PCIE 306 signals in the low bytecable 302, and the high byte control 312 and high byte PCIE 310 signalsin the high byte cable 304 are conveyed optically utilizing a respectiveoptical transceiver (XCVR) 318 on the cable card 140 and opticaltransceiver (XCVR) 358 in the IO drawer 106. The PCIE lanes 0 to 7conveyed on the low byte PCIE 306 and lanes 8 to 15 conveyed on the highbyte PCIE 310 commonly pass through a PCIE re-timer 320 in FIG. 3A, aPCIE re-timer 360 in FIG. 3A in order to synchronize them with therespective optical transceivers 318, 358 shown in FIGS. 3A and 3B.

The local control FPGA 210 on the cable card 140 includes a local FPGAdata engine 322, registers 324, a link engine 326, and a wire engine328. The remote control FPGA 250 similarly includes a remote FPGA dataengine 362, registers 364, a link engine 366, and a wire engine 368, andoptionally a flash memory 370 coupled to the data engine 362. The localcontrol FPGA data engine 322 and remote control FPGA data engine 362 arecapable of exchanging control signals utilizing either the low bytecontrol 308 or high byte control 312 conveyed over the low byte cable302 or high byte cable 304, respectively. The local control FPGA 210link engine 326 utilizes the data engine 322 to establish reliableoptical signaling and bit transfer protocols between the optical XCVRs318 on the cable card 140 and the optical XCVRs 358 and data engine 362in the IO drawer 106 over both of the low byte cable 302 and high bytecable 304.

The wire engine 328 of local control FPGA 210 receives the state ofcertain bits of the registers 324 or DC voltage signals and utilizes thedata engine 322 to transmit these states to the registers 364 of theremote control FPGA 250. The registers 324 include a predefined bit toassert the state of the PCIE auxiliary PERST DC voltage signal outputfrom a PHB 130 to a device attached to the respective PCIE link, and abit to receive the state of PCIE auxiliary device present DC voltagesignal from a PCIE slot 152 or PCIE switch 156 in the IO drawer 106connected to the PCIE link over the low byte cable 302 and high bytecable 304. When the state of certain bits of registers 324 changes, thewire engine 328 of the local control FPGA 210 automatically communicatesthese to registers 364 of the remote FPGA 250. The wire engine 368 ofremote control FPGA 250 receives the state of certain bits of theregisters 364 or DC voltage signals and utilizes the data engine 362 totransmit these states to the registers 324 of the local control FPGA210. Whenever the state of these certain bits of registers 364 changes,the wire engine 368 automatically communicates these to registers 324 ofthe local control FPGA 210.

The respective wire engine 328, 368 on each end of the optical cables302, 304 provide an alternative signaling mechanism for PCIE auxiliarysignals or other DC voltage signals within the fiber optic cables toestablish or receive the active or inactive state of the auxiliarysignals at the respective other end of the cable.

The registers 324 of local control FPGA 210 include bits representingvarious properties of the cable card 140, such as the type of the cablecard itself, the type and connection states of the low byte cable 302and high byte cable 304. The registers 324 of the local control FPGA 210include bits to detect the states of certain hardware inputs from orcontrol the states of certain hardware outputs to the components of thecable card 140. The registers 324 of local control FPGA 210 include bitsrepresenting various properties of the cable connections to that TOdrawer, such as representing which location on the TO drawer 106 of thelow byte cable 302 and high byte cable 304 are connected, to enablefirmware to determine that cables are properly connected.

The cable card 140 and the TO drawer 106 optionally includes Link ActiveLEDs 380 in association with each of the low byte cable 302 and highbyte cable 304. Firmware operating in the CEC 102 utilizes bits withinthe registers 324 of the local control FPGA 210 to active or deactivatethe link active LEDs 380 to indicate that the cable is or is notactively transmitting signals between the cable card 140 and IO drawer106. It should be understood that hardware mechanisms may alternativelybe utilized to detect link transmission activity and to accordinglyactivate or deactivate link active LEDs 380. Firmware operating in theCEC 102 performs other control and communications operations, such asactivating or deactivating power to the IO drawer 106, a bay 150, or abay 154, PCIE slots 152, or other components within the IO drawer 106.

Referring to FIG. 4, there are shown example operational featuresgenerally designated by the reference character 400 of a physical layerview of the example system 100 of FIG. 1 in accordance with a preferredembodiment. An I2C multiplexer (MUX) 402 connects to an I2C bus 406 anda respective data engine 404, 414 and an I2C SPI flash logic 410, 420 athost side FPGA 210 and IO drawer side FPGA 250 are shown connected byCXP lanes. A respective SPI flash 412, 422 is coupled to the I2C SPIflash 410, 420 at host side FPGA 210 and IO drawer side FPGA 250. TheI2C multiplexer (MUX) 402 and the respective data engine 404, 414 enablesystem firmware to access secondary I2C buses in either the host FPGA210 or IO drawer FGPA 240 in a consistent manner. The secondary I2C buscould be one of the I2C buses 254 of FIG. 3B communicating to I2Cdevices within the IO drawer 106 or it could be one of the I2C buses 204of FIG. 3A communicating to the I2C devices of the cable card 140.

Referring to FIG. 5, there is shown a flow chart illustrating examplefirmware operational features using sideband status information of theexample system 100 in accordance with a preferred embodiment.

As indicated in a decision block 500, checking for a PCIE card presentin CEC PCIE slot is performed. When a PCIE card is not present in CECPCIE slot, then operations return as indicated in a block 501. When aPCIE card is present in CEC PCIE slot, the cable card present portexpander is read as indicated in a block 502. As indicated in a decisionblock 504, again checking for the PCIE cable card present in CEC PCIEslot is performed. When a PCIE cable card is not present in CEC PCIEslot, then operations return at block 501.

When a PCIE cable card is present in CEC PCIE slot, the local FPGAregisters are read to get cable status and connection locations asindicated in a block 506. Checking if the cable card includes a pair ofcables or dual cables is performed as indicated in a decision block 508.When the cable card includes dual cables, checking is performed todetermine if the high byte control is working as indicated in a decisionblock 510. If the high byte control is not working, a cable error islogged for service as indicated in a block 512. If the high byte controlis working and when the cable card does not include dual cables,checking is performed to determine if the low byte control is working asindicated in a decision block 514. If the low byte control is notworking, a cable error is logged for service as indicated in a block516.

As indicated in a block 518, local FPGA registers are read to verifycables are correctly connected low to low, high to high, and same PCIElink connection at the IO drawer. Checking if cabled correctly isperformed as indicated in a decision block 520. If not cabled correctly,a cable error is logged for service as indicated in a block 522. Ifcabled correctly, PERST to the IO drawer PCIE link connection isde-asserted as indicated in a block 524. Checking is performed todetermine if connected to PCIE switch in IO drawer as indicated in adecision block 526. When connected to PCIE switch in IO drawer, the PCIEswitch and downstream PCIE links to PCIE slots in the IO drawer areconfigured as indicated in a block 528. The PCIE slot or PCIE slots inthe IO drawer under the PHB connected to this cable are configured asindicated in a block 530 following block 528 and following decisionblock 526 if not connected to PCIE switch in IO drawer. The PCIE linkconnection configuration is complete as indicated in a block 532.

Referring to FIGS. 6A and 6B, there is shown example PCI bus generallydesignated by the reference character 600 of the example system 100 inaccordance with a preferred embodiment. The illustrated PCI bus 600provides a path from a PCIE host bridge (PHB) 602 to an optical cableattached IO drawer 106. For example, two industry standard 12 laneoptical cables are used to carry PCIE and sideband traffic between thesystem PHB 602 and the IO drawer 106. Each cable contains 8 lanes ofPCIE traffic, 1 channel of sideband communication and 1 spare opticalchannel with two channels unused. With one cable carrying PCIE lanes 0-7(low byte) and the other carrying PCI lanes 8-15 (high byte) togetherthey make an x16 PCIE bus connection to the IO drawer 106. The one spareoptical channel per cable in each direction allows firmware to route asingle PCIE lane away from a faulted channel to the spare channel whenfirmware determines a channel that is faulted. Other implementationscould use, for example two unused channels as spares for the PCIE linksas well. Other embodiments could also use, for example, more than 2cables each cable carrying fewer than 8 of the 16 PCIE bus signal lanes,and spare optical channels for those lanes, and two or more of thosecables also carrying redundant sideband communication signals.

As shown in FIG. 6A, PCI bus 600 includes a PCIE retimer 604, fieldprogrammable gate array (FPGA) communication devices 606, lane sparingmultiplexers (muxes) 608 including lane sparing transmit (TX) muxes 610,and lane sparing receive (RX) muxes 612, and High and Low optical moduletransceivers (CXPs) 614, 616 with respective optical connections X9+DN,SB, X9+UP, SB. With respect to the cable card end of the cable X9+DNrepresents nine PCIE optical transmit channels, eight active plus onespare, and X9+UP represents nine PCIE optical receive channels, eightactive plus one spare, and wherein each transmit channel is paired witha receive channel to form a single bi-directional PCIE lane. Forexample, with each industry standard optical cable containing 12channels of bidirectional traffic, eight of those channels optionallyare used for PCIE, one used for sideband communication SB and one of thethree unused channels wired to be used as a spare PCIE lane. As shown,the FPGA communication devices 606 are connected to the PCIE retimer604, High and Low optical module transceivers (CXPs) 614, 616, and thelane sparing multiplexers (muxes) 608.

As shown in FIG. 6B, PCI bus 600 includes High and Low optical moduletransceivers (CXPs) 620, 620 that are connected to the High and Lowoptical module transceivers (CXPs) 614, 616 of FIG. 6A with therespective optical connections X9+DN, SB, X9+UP, SB. With respect to theIO drawer end of the cable, X9+DN represents nine PCIE optical transmitchannels, eight active plus one spare, and X9+UP represents nine PCIEoptical receive channels, eight active plus one spare, and wherein eachtransmit channel is paired with a receive channel to form a singlebi-directional PCIE lane. PCI bus 600 includes lane sparing multiplexers(muxes) 624 including lane sparing transmit (TX) muxes 626, and lanesparing receive (RX) muxes 628; a PCIE retimer 630, field programmablegate array (FPGA) communication devices 632, and a PCIE switch 634 ofthe IO drawer 106. As shown, the PCIE switch 634 is connected to aplurality of PCI slots 636 #1-N, for example, 6 PCI slots 636 of the IOdrawer 106. As shown, the FPGA communication devices 632 are connectedto the PCIE retimer 630, High and Low optical module transceivers (CXPs)620, 620, lane sparing multiplexers (muxes) 624, and connected to thePCIE switch 634, a drawer controller (CMC) 638 and the PCI slots 636 ofthe IO drawer 106.

Referring to FIG. 7 there is shown example lane sparing hardwaregenerally designated by the reference character 700 of the examplesystem 100 in accordance with a preferred embodiment. Lane sparinghardware 700 is used to reroute PCIE lanes to a spare optical channel onboth ends of the optical path in accordance with a preferred embodiment.As shown, lane sparing hardware 700 includes an I2C port expander device702 coupled to an optical transceiver (CXP) connector 704 by a CXPinterface block 706.

The I2C port expander device 702 is used to control a set of PCIE lanemultiplexers (muxes) 708, 710. As shown, lane sparing hardware 700includes a retimer 714 coupled to the PCIE lane muxes 708, 710, a fieldprogrammable gate array (FPGA) 716 coupled by sideband and SM bus to theCXP interface block 706 and CXP connector 704 and coupled to the I2Cport expander device 702. Lane sparing hardware 700 includes control andstatus registers 718 included with the CXP connector 704.

Interrogating PCIE retimers in either the cable card 140 or IO drawer206 ends of a cable, such as retimer 714 can be used to determine afaulted optical channel. For example, by reading retimer registers it ispossible to determine for each PCI lane what stage of the PCIE linktraining sequence has been initiated. System firmware can use thisinformation to determine if one lane has not progressed at all whichthen indicates a bad optical channel. By reading transmit statusregisters in the optical transceivers of either the cable card 140 or IOdrawer 106 it is possible to determine for each optical channel if afault has occurred. This information can be used to determine a badoptical channel. By reading receiver status registers 718 in the opticaltransceivers 704 of the IO drawer 106 it is possible to detect a loss ofsignal from the respective cable card 140 transceiver and thisinformation can be used to determine a bad optical channel.

By programming muxes in the PCIE path firmware can reroute PCIE awayfrom the faulted channel. The I2C port expander device 702 is controlledthrough the FPGA 716, for example using I2C communication through thesideband signals. When the I2C port expander device 702 is programmed byfirmware it changes the input to output mapping of the PCIE lane muxes708, 710 which causes the PCIe bus to be rerouted down a differentoptical channel. When the operation is complete a reset sequence can beinitiated on the PCIE bus incorporate the spare channel into the link torecover to its optimal width.

Referring to FIG. 8, there are shown example operations for implementingcable failover in multiple cable Peripheral Component InterconnectExpress (PCIE) IO interconnections in accordance with a preferredembodiment starting the PCIE link health check as indicated in a block800. Checking is performed, for example, periodically or as a result ofa hardware interrupt to determine if the PCIE link is degraded, asindicated in a decision block 802. When the PCIE link is not degraded,then the operations are completed as indicated in a block 804. When thePCIE link is degraded components are interrogated to determine if afaulted low byte cable exists as indicated in a block 806.

Checking is performed to determine if a faulted low byte cable isdetected as indicated in a decision block 808. When a functional highbyte cable is not detected, then the operations are completed asindicated in a block 810.

When a faulted low byte cable is detected, components are interrogatedto determine if a functional high byte cable exists as indicated in ablock 812. Checking is performed to determine if a functional high bytecable is detected as indicated in a decision block 814. When afunctional high byte cable is not detected, then the operations arecompleted as indicated in a block 816.

When a functional high byte cable is detected, then a PERST is assertedto the PCIE link as indicated in a block 818. The low byte cable isdisabled as indicated in a block 820. The PCI host bridge (PHB) isreconfigured to reverse the PCIE lane order as indicated in a block 822.The PERST is deasserted and the PCIE links are retrained as indicated ina block 824. The operations are completed as indicated in a block 826.

It would be obvious to extend the sequences of FIG. 5, and FIG. 8 andthe structures of FIGS. 6A, 6B, and 7 to an embodiment utilizing morethan 2 cables between a cable card 140 in a CEC 102 and a slot 152 orswitch 156 in an IO drawer 106. It would be obvious to extend thepresent invention to signaling or IO interconnections other than PCIEwhere optical cabling is utilized to convey such signals.

Referring now to FIG. 9, an article of manufacture or a computer programproduct 900 of the invention is illustrated. The computer programproduct 900 is tangibly embodied on a non-transitory computer readablestorage medium that includes a recording medium 902, such as, a floppydisk, a high capacity read only memory in the form of an optically readcompact disk or CD-ROM, a tape, or another similar computer programproduct. Recording medium 902 stores program means 904, 906, 908, and910 on the medium 902 for carrying out the methods for implementingcable failover in multiple cable Peripheral Component InterconnectExpress (PCI-Express or PCIE) IO interconnections attached to an IOdrawer 106 of preferred embodiments in the system 100 of FIG. 1.

A sequence of program instructions or a logical assembly of one or moreinterrelated modules defined by the recorded program means 904, 906,908, and 910, direct the computer system 100 for implementing cablefailover in multiple PCIE IO interconnections attached to an IO drawer106 of a preferred embodiment.

While the present invention has been described with reference to thedetails of the embodiments of the invention shown in the drawing, thesedetails are not intended to limit the scope of the invention as claimedin the appended claims.

What is claimed is:
 1. A method for implementing cable failover inmultiple cable Peripheral Component Interconnect Express (PCI-Express orPCIE) IO interconnections attached to an IO drawer in a computer system,comprising: providing system firmware for periodically implementinghealth check functions and responsive to a hardware interrupt todetermine if the PCIE link is degraded and detecting a degraded PCIElink; providing multiple cable PCIE IO interconnections coupled betweena PCIE host bridge (PHB) and an PCIE enclosure, providing PCIEmultiplexer logic coupled between said PHB and the multiple cable PCIEIO interconnections; identifying a faulted low byte cable and performinga full lane reversal of the PCIE lanes including issuing a FundamentalReset, and PCIE clocks to said multiple cable PCIE IO interconnectionsfrom said PHB to said PCIE enclosure, deasserting said Fundamental Resetand retraining the PCIE links.
 2. The method as recited in claim 1,includes providing system firmware for implementing health checkfunctions for PCIE IO interconnections to identify a faulted low bytecable.
 3. The method as recited in claim 2, includes interrogatingcomponents to determine if a faulted low byte cable exists.
 4. Themethod as recited in claim 3, includes providing system firmware forimplementing health check functions for PCIE IO interconnections toidentify a functional high byte cable.
 5. The method as recited in claim4, includes interrogating components to determine if a functional highbyte cable exists.
 6. The method as recited in claim 5, whereinperforming a full lane reversal of the PCIE lanes is responsive toidentifying a functional high byte cable.
 7. The method as recited inclaim 1, wherein performing a full lane reversal of the PCIE lanesincluding issuing a Fundamental Reset includes issuing a PCI ExpressReSeT (PERST) to the PCIE IO interconnections.
 8. The method as recitedin claim 7, includes disabling the low byte cable.
 9. The method asrecited in claim 8, includes reconfiguring the PHB to reverse the PCIElane order.
 10. The method as recited in claim 1, wherein providing PCIEmultiplexer logic coupled between said PHB and the multiple cable PCIEIO interconnections includes providing PCIE lane multiplexers to reversethe PCIE lane assignments from the PHB to the external PCIE cables andlogic to control the PCIE lane multiplexers through system firmware. 11.The method as recited in claim 1, includes providing downstream PCIEdevices to support running in normal lane mode and a lane reversed mode.